The calculator applies a formula based on the structure of the lesson to figure out a group rate. The lesson structure is like this: half of any given lesson is information and watching the teacher perform certain techniques. The other half is more interactive, in which the teacher actually observes the student's movements, corrects them, and personally tailors the lesson experience to them.

In a group situation, the first half (information, watching teacher) is obviously useful to anyone present. For that matter, each student in a group pays fully one half the price of a normal single person lesson. The second half (teacher attending to student) is devalued with multiple people present, though. The total time available for personal tailoring is divided amongst all students present. Thus, students only individually pay their share.

The formula which expresses this is:

0.5*P*N + 0.5*P = GP

Where

P = Price of One Person Lesson or One Person Lesson Package.
N = Number of Students in the Group (you input this data).
GP = Group Price, as calculated by the formula.